Radio receiver with logarithmic response circuit



mi! 17, 1 951 E. o. SCHREINER ETA!- 5 9 RADIO RECEIVER WITH LOGARITHMIC RESPONSE CIRCUIT File l April 17, 1946 2 Sheets-Sheet 1 OUTPUT VOLTAGE LOG SCALE l-O I0. I00.

INPUT VOLTAGE I INVENTORS EDMUND D. SCHREINER YBRADFORD HOWLAND ATTORNEY April 1'], 1951 E. D.,scI-IREINER ETAL 2,543,913

RADIO RECEIVER WITH LOGARITHMIC RESPONSE CIRCUIT Filed April 17, 1946 x 2 Shuts-Sheet. 2

2o OPERATING PORTION VOLTS I0 I 30 20 I 5 30 LET... 5

RF NON LINEAR TO HALF WAVE AMPLIFIER MIXER CIRCUIT -AMPLIFI R-- STAGE RECTIFIER AW. E D TECTOR LOCAL OSCILLATOR AT'I' URNE Y Patented Apr. 17, 1951 RAmo RECEIVER WITH LoG Ir MIO- RESPONSE oinou r Edmund D. Schreiner, washing-ton Di 0., and

Bradford'flowland,LaFayette,Ind: 1

Application April 17, 1946, Seria lNo. 662,166

(Granted under the act oi March; 3, 1883, as amended; April 30; 1928;; 3700. G.. 7-57).

This invention relates to voltage control cir- Quite an o a cu arl e. lt e ntr object of this invention is to providean setan aneou mea o automa ca om ress,-

ing the range oi voluine of modulatedvoltagesin order ot o load Qra urate c c t -eo neeted o.. h u u h r a Another object of this invention is; to provide.

anj nst n a ee e ct n aut m t e ume ene trol means, that is simple, light andcompact and having no easily breakable. parts.

Automatic volume control. circuits of A the prior artsene al v s feed ac r m a e e i lae r eq n mp ifie tubes; an nc ora a ime ela to eve t-te iaetaaetiem an enera1l-- so ha c ndense s. the cir uit er; filterin :p r e;-. nany pli t e Where im de ay o ec ona l onvent al ei cui e n:

volving the charging and discharging of con-..

densersare not desirable.

The methodused in attaining these objectshas been to apply-the .voltageldesired to be controlled;

to..a nonlinear. devicei; e. one whoseimpedance is nota constant but changes under different conditions-of. current and voltage. One example, of such-adevice is a crystal diode such as that commerciallydesignated: as 1N34. In general, it is necessary to operate on a portion of the impedance characteristics of this device where the impedance changesrapidly with changes of voltage i. e. where a large change in input voltage iscompressed toa small change in; output voltage. To operate on this portionofthecurveitis-necessary; toincorporate the nonlinear devices in a network. Several-nonlinear devices may be used in shunt to obtain the desired output:

The nonlinear device, where it is incorporated into a substantially logarithmic response network maybe used as an automatic volume control cir- Quit; by inserting the logarithmic response circuit inseries with other radio frequency stages. This nr lves no. ee k n ub a t a no ime ela x p for heehare s o 1she as ociated ea e tan e Q th n earde iee whi i oi. e. rder. Qf. mierQ-miereiarade for a. y ical:

crystal diode. Figure 1 is a schematic diagram of a typical mbedimeat: h nvention-- Figurerzis-a schematic; diagram of another typical embodiment of the invention.

Figure 3.- e grease; si nal; n ut. signal ieh vi s ane t ut es hmi a z tbe: vits he r. in u and. havi g n gl b e ime.

output; showing the operatingcharacteristic; of

the circuitsofFigure 1 andiFigure 2.

Figure 4 shows a typical characteristic curve of a nonlinear device, and:

Figure 5 is a. block diagram ofthe invention usedas anautomatic volume control circuit in a radio frequency receivingsystem.

In reference-to Figure 1-; anexemplary embodiment of this invention is shown, comprising; a

pair of input terminals. 20- and: 21; a. connection including a fixed impedance 22, a biasing source 24; and a crystal diode 23 allconnected in seriesacrossthe input terminals, and a panel? outputtermina-ls 25 andf2ficonnected across the crystal diode 23 and the biasing-source 24';

The generalprincipleof operation ofi-this circuitis somewhat anal' l ous tothatof an ordinary voltage divider circuit, except. that, it; iscome. plicated by the fact. that it; isthe; property of; the nonlinear. impedance element; 23 to;change; its impedancein response-to theamplitude of. H183 applied signal across .terminalslll and! I Name- 1y, theimpedance of. the nonlinear impedance ele-.

ment 23, diminishes .withincreased signal. amplit tude. Consequently by, exer isingtsome control Over he m da e. char ct ris c. f. diode 2.3 uc s meane i h ia i ource shown as a battery and by properly selectin impedance element 22, in relation,v tothe impedance of the diode 23, the voltage divider action of the circuit can be made so as to causeinput signals, below a certain positive amplitudeandnegatiye signals, to appear at the outputterminals fi and 26.;w ith. substantially full amplitude. Whereas positive.

input signals having an amplitude above the same certain amplitude will cause the impedance of the diode 23 to diminish and; consequently will.

appear at the output terminals very much compressed in amplitude, and in the circuitoi Figure 1, the output signals have approximately a log-;

arithmic relation to'the input signals. The cutoff level below which input'signals will appear sub stantially unattenuated at the output terminals,

is establishedby selecting a'voltage for'the-direct' current source 24-such as to cause the diode 213,

to operate at a point-of itscharacteristic curve, j

as indicated: on Figure 4 where the diode has substantially an infinite impedance, below that point.

Inputsignals which areof such an amplitude, K as to drive the operatingpoint-of the crystal diode; to; the right on thelcurveaoi l 'igure 4, cause the;

impedance. ofthe. diode to drop, which consequently reduces the. output signal toa value; which .approaches: a logarithmic relationto the input signal. A curve which illustrates the approximate relationship between the input and the output voltages of the circuit of Figure 1 is shown as curve B in Figure 3. The embodiment illustrated in Figure 2, to which reference is now made, consists of two sections, connected in cascade, each similar to the circuit of Figure 1, the input section across input terminals I and 2, comprises a resistor 3, in one side of the line, followed by a resistor 5, a nonlinear device 1, and a D. C. voltage source 9, all three in series across the line. The path of easy current flow is as indicated from the resistor 5, to the nonlinear device and to the plus side of the D. C. voltage source.

The second, or output section consists of a resistor 4, in the same side of the line as resistor 3, and connected to the junction of resistor 3 and resistor 5, followed by the nonlinear device 8, in series with the D. C. source If), across the line and also across the output terminals H and I2. The path'of easy current flow is from the nonlinear device to the plus side of the D. C. voltagesource. The D. C. voltage sources 9 and I introduce a voltage delay in the operation of their associated nonlinear devices. source 9 is greater than H). The bias voltages further provide a voltage delay or a minimum level, below which the respective diodes represent substantially infinite impedances.

When E in exceeds voltage source 10, but not voltage source 9 current will flow through resistor 3, resistor 4, and nonlinear device 8, and the voltage developed across nonlinear device 8, plus that of source ill will appear across terminals H and I2 shown as E out.

If the input voltage exceeds voltage source 9, current will flow from terminal I through resistor 3, resistor 5, nonlinear device I, voltage source 9, hack to terminal 2. The voltage developed across resistor 5, plus that developed across nonlinear device 1, plus that of voltage source 9, will then appear across points l3 and I4. If this voltage is less than voltage source 10, it will eso appear across the output terminals H and greater than sourc [0, current will fiow through nonlinear device 8, and the voltage across the nonlinear device 8, plus that across the voltage source 10, will appear as E out across terminals II and I2. mate relationship between the input and output voltages of the circuit of Figure 2 is shown at A in Figure 3. By suitably choosing the conponents, th number of sections, and the biasing voltages with respect to the output characteristics desired and the input characteristics specified, great flexibility may be obtained.

Figure 5, to which reference is now made, shows in block diagram form the utilization of the logarithmic response circuit as an automatic volume control circuit, in combination with other components of a modulated carrier wave system. Radio frequency energy is received from the antenna 30 by the R. F. amplifier 3i, and fed to the mixer 32, and then to the half wave rectifier 33, thru the logarithmic response network 34 to the amplifier 35, and to the second detector. If the input signal, to the logarithmic response network, has both positive and negative components, with reference to the operatmg point on the characteristic curve, the positive portions will be attenuated logarithmically, and the negative portions will not be attenuated. Therefore it is necessary to rectify the modu- In Figure 2 the D. C. voltage If the voltage across points l3 and I4 is A curve illustrating the approxilated signal and apply it to the logarithmic response network as a unidirectional signal.

If a voltage of the form;

E=A(1+m sin wt) is fed into the logarithmic response network; where A=Input signal strength factor m=Percent modulation Then the output of the automatic volume control circuit will be substantially as follows;

E out (1. Log E in E out 0. Log A(1+m sin wt) E out or. Log A+Log (1+m sin wt) It is noted that change in the input signal strength A, does not influence the amplitude of the modulation component, (1+m sin wt). Therefore the desired component, the modulation, will be held constant even though the signal level A changes.

Although we have shown and described only limited and specific embodiments of the present invention we ar fully aware of the many modifications possible thereof. vention is not to be limited except insofar as is necessitated by the spirit of the prior artand the scope of the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

What is claimed is: 1. A modulated wave carrier receiving system comprising an amplifier section, a demodulator,

a half wave rectifier connected to the output of the said amplifier section and a logarithmic response network connecting the output of said rectifier to th demodulator of said receiving system, said last named network comprising, a pair of input terminals, 9. first series connection across said input terminals, said connection in-- cluding an impedance element, and a nonlinear impedance device, a second series connection also including an impedance element and a nonlinear impedance device connected in shunt with a portion of the said first series connection, and a pair of output terminals connected across said nonlinear impedance device of said second series connection.

2. A modulated carrier wave receiving system comprising an amplifier section, a demodulator, a half wave rectifier connected to the output of the amplifier section and a logarithmic response network connecting the output of said rectifier to the input of said demodulator comprising a pair of input terminals and a pair of output terminals, an impedanceless connection between one terminal of the input and output pairs, a high impedance connection between the other terminal of the input and output pairs, and a series connection comprising a diode non-linear impedance device and a biasing source connected; across the ouput terminals, said biasing source.

being disposed to oppose the flow of current through said diode impedance device and'proportioned to provide said device with a normally high impedance under low amplitude'signalconditions.

EDMUND D. SCHREINERQ BRADFORD HowLAN (R r c s 0 9ll9win: me)

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